Oxide thin films

To obtain high quality samples of complex oxides, we fabricate epitaxial layers and heterostructures of these compounds by optimized pulsed laser deposition. With this technique, films and multilayers can be grown from a broad spectrum of materials, thereby maintaining structural control down to atomic dimensions.

These samples are patterned by optical- or electron-beam lithography and ion-beam etching, and are electrically and magnetically characterized. Part of this effort is devoted to analyse the behavior of interfaces in complex materials, such as interfaces in magnetic multilayers or grain boundaries in high-T_c superconductors.

It is important to understand the physics and materials science of these grain boundaries, since they limit the performance of superconducting cables. Further, the grain boundaries form excellent Josephson junctions. Intriguingly, these junctions are controlled by the d-wave symmetry of the macroscopic quantum mechanical wave function of the superconductor, which therefore directly affects the current rating of superconducting cables!

Another important part of our research is interfaces in oxides, which have properties that differ from those found in the bulk of the constituting materials. A fascinating example for this is the interface between the two insulators Lanthanumaluminate and Strontiumtitante (an artistic view is shown in the image below). A conducting electron gas (green) is formed at the interface, but only if the thickness of the Lanthanumaluminate exceeds three unit cells. The conductivity can be tuned to a large extent by applying a gate field.